Heat sink for an electronic power component

ABSTRACT

A heat sink comprising a body made of a metallic material with good thermal and electricity conduction properties having a surface intended to support an electronic power component forming a heat source. The body comprises a plurality of openings axially crossed by tubes of circulation of a cooling liquid. Each tube being formed of a material with a good thermal conductivity and being separated from the body by a ring-shaped electric isolation layer formed of a compressed powder of at least one material with good electric isolation and thermal conduction properties.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a heat sink for an electronic power component, for example, a thyristor, a triac, a MOS power transistor, or an insulated gate bipolar transistor (IGBT). More specifically, the present invention relates to a heat sink in which a cooling liquid is circulated to carry off calories provided by the electronic power component.

2. Discussion of the Related Art

The heat sink must ensure three main functions:

-   -   mechanically mounting the component to be cooled down;     -   carrying off calories provided by the component; and     -   electrically isolating the component from the cooling liquid.

A conventional heat sink generally comprises a parallelepipedal body on which is mounted the component to be cooled down, and which is formed of a material with a good thermal conductivity. To ease the component assembly on the component and avoid generation of thermal resistances, the material forming the heat sink body generally also is a good electric conductor. It generally is metal, for example, copper or aluminum. The body is crossed by parallel cylindrical openings containing tubes conducting the cooling liquid.

French application 2,729,044 filed by Atherm Company describes a heat sink in which each tube is formed of an electric isolator to electrically isolate the cooling liquid from the electronic power component. Each tube is separated from the corresponding opening of the heat sink body by a gap filled with a metal alloy, to optimize the thermal exchange between the electronic power component and the cooling liquid.

It may however be difficult to find for all tubes a material which provides a convenient compromise between a good electric isolation and a good thermal conductivity. Indeed, each tube must have walls of a thickness greater than a minimum thickness to obtain a sufficient electric isolation and to have a sufficient mechanical hold, especially to simplify the tube handling and assembly. This tends to decrease the thermal conductivity properties of the tube.

Further, the manufacturing of such a heat sink is relatively complex, especially to ensure a good mounting of the tubes with respect to the heat sink body.

Further, according to French application 2,729,044, the heat sink may comprise, in each tube, means for guiding the cooling liquid flow in the tube, called a “turbulator”. Turbulators enable increasing the local Reynolds coefficient of the cooling liquid flowing in the tubes to increase thermal exchanges between the cooling liquid and the tubes. The turbulators are maintained in the associated tubes via screws, which increases the complexity of the assembly of such a heat sink.

SUMMARY OF THE INVENTION

The present invention aims at obtaining a heat sink for an electronic power component comprising a heat sink body, on which the component is assembled, crossed by tubes conducting a cooling liquid flows, the heat sink enabling increasing thermal exchanges between the cooling liquid and the heat sink body.

Another object of the present invention consists of improving the electric isolation of the cooling liquid with respect to the component.

Another object of the present invention consists, in the case where the cooling tubes are equipped with turbulators, of easing the turbulator assembly.

To achieve these objects, the present invention provides a heat sink comprising a body made of a metallic material having a surface intended to support an electronic power component, the body comprising a plurality of openings axially crossed by tubes of circulation of a cooling liquid, each tube being formed of a material with a good thermal conductivity and being separated from the body by a ring-shaped electric isolation layer formed of a compressed powder of at least one material with good electric isolation and thermal conduction properties.

According to an embodiment of the present invention, each tube is made of metal.

According to an embodiment of the present invention, the compressed powder is a boron nitride and/or aluminum nitride powder.

According to an embodiment of the present invention, the heat sink further comprises, at least in a tube, guiding means intended to accelerate the cooling liquid flow in contact with the tube are made of a material with a good thermal conductivity.

According to an embodiment of the present invention, the guiding means is only maintained by contact with the tube.

According to an embodiment of the present invention, the guiding means comprise a cylindrical portion on the circumference of which extend grooves separated by teeth, the grooves being adapted to the flowing of the cooling liquid, the teeth being in contact with the tube.

The present invention also provides a method for manufacturing a heat sink, comprising the steps of:

-   -   a) providing a heat sink body made of a metallic material having         a surface intended to support an electronic power component, the         body being crossed by a plurality of openings;     -   b) placing in each opening a tube separated from the opening by         a ring-shaped gap;     -   c) filling each ring-shaped gap with a powder of at least one         material with good electric isolation and thermal conduction         properties; and     -   d) compressing the powder in each gap.

According to an embodiment of the present invention, step b) comprises, for each opening, the arrangement of a tubular jointing sleeve crossed by an orifice at one end of the opening, the tube being maintained in the orifice of the jointing sleeve distantly from the body, the powder being then introduced, at step c), through the ring-shaped gap at the level of the axial end of the opening opposite to the jointing sleeve.

According to an embodiment of the present invention, step d) is followed by the arrangement of an additional tubular sleeve at the level of the end of the opening through which the powder has been introduced.

According to an embodiment of the present invention, the method comprises before step c), the arrangement of guiding means in at least one tube, the powder compression being performed to deform the tube so that it comes into contact with and maintains in place the guiding means.

The foregoing objects, features, and advantages of the present invention, as well as others, will be discussed in detail in the following non-limiting description of specific embodiments in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified perspective view of an example of the forming of a heat sink according to the present invention on which is assembled an electronic power component to be cooled down;

FIG. 2 is a top view of the heat sink of FIG. 1;

FIG. 3 is a cross-section view of FIG. 2 along line III-III;

FIG. 4 is an enlargement of a portion of FIG. 3;

FIG. 5 is a cross-section view of FIG. 4 along line V-V; and

FIG. 6 is a simplified perspective view of an example of the forming of a turbulator.

DETAILED DESCRIPTION

FIG. 1 schematically shows an example of the forming of a heat sink 10 according to the present invention, comprising a parallelepipedal body 12, formed of a material which is both a good thermal conductor and a good electric conductor, for example, copper or aluminum, on which is attached an electronic power component 14 to be cooled down.

FIG. 2 is a top view of heat sink 10. Body 12 is crossed by parallel openings, not visible in FIG. 2, of circular cross-section, in which flows a cooling liquid, for example, glycol water. The circulating of the liquid is ensured by an intake manifold 16 and an exhaust manifold 18. Isolating connections 20, 21, for example, made of silicon, are provided between body 12 and manifold 16, 18.

FIG. 3 is a cross-section view of FIG. 2 along line III-III formed at the level of an opening 22 crossing body 12 of the heat sink. The structure described hereafter is identical for each opening 22 of body 12 of the heat sink. Opening 22 contains a metal tube 24, for example, made of copper or aluminum, corresponding to a good thermal conductor, which is separated from opening 22 by a gap 26. As an example, tube 24 has a radial thickness on the order of 0.5 mm and the gap has a radial thickness on the order of 2 mm. Gap 26 contains a compressed powder formed of a material which corresponds to a good electric isolator and to a good thermal conductor. The powder may also be formed of a mixture of materials that each correspond to a good electric isolator and to a good thermal conductor. It is for example boron nitride or aluminum nitride. Tube 24 comprises a first end portion 28 which prolongs out of opening 22 and which is mounted to intake manifold 16 and a second end portion 30 which prolongs out of opening 22 and which is mounted to exhaust manifold 18. The connection between each end portion 28, 30 of tube 24 and intake manifold 16 and exhaust manifold 18 may be formed by any known method, for example, by welding or by soldering. On either side of body 12 of the heat sink, a portion of end portions 28, 30 of tube 24 protruding out of body 12 is surrounded with an isolating jointing sleeve 32, 34, for example, made of glass fiber, slightly penetrating into opening 24 of body 12, between tube 24 and body 12. Isolating connections 20, 21 surround end portions 28, 30 of tube 24 and a portion of isolating sleeves 34 between body 12 and manifolds 16, 18 to prevent the forming of electric arcs between body 12 and tube 24. A turbulator 36, having the shape of a full profile, is arranged in tube 24. Turbulator 36 delimits with the tube ducts 38, extending along the entire length of opening 22, conducting the cooling liquid.

Inlet and exhaust manifolds 16 and 18 comprise internal openings, not shown, arranged to obtain a specific type of flow of the cooling liquid in body 12 of the heat sink. According to a first example, intake manifold 16 and exhaust manifold 18 may each comprise an opening into which all tubes 24 emerge so that the cooling liquid simultaneously flows in each tube 24 from intake manifold 16 to exhaust manifold 18. According to a second example, intake manifold 16 and exhaust manifold 18 comprise orifices connecting tubes 24 in pairs so that the cooling liquid zigzags successively from a tube to an adjacent tube.

FIG. 4 is an enlarged view of a portion of FIG. 3 at the level of an end of tube 24. Opening 22 divides into a main opening 39 of constant circular cross-section which prolongs at each end in an end opening 40, of larger diameter, connected to main opening 39 by a shoulder 41. Each isolating end sleeve 34 comprises a main tubular portion 42 having its external diameter corresponding to the inner diameter of end opening 40 and having its inner diameter corresponding to the outer diameter of tube 24. Main tubular portion 42 prolongs in a secondary tubular portion 43 having its outer diameter corresponding to the inner diameter of end opening 40 and having its inner diameter substantially corresponding to the inner diameter of main opening 39. Secondary tubular portion 43 abuts against shoulder 41, a portion of main tubular portion 42 then extending out of opening 22.

FIG. 5 is a cross-section view of FIG. 4 along line V-V and FIG. 6 is a perspective view of turbulator 36. Turbulator 36 has the shape of a cylindrical tree of axis D on the circumference of which are distributed teeth 45 which extend parallel to axis D along the entire length of turbulator 36. Passages 38 delimited between turbulator 36 and tube 24 correspond to the grooves between two adjacent teeth 45. Turbulator 36 enables locally increasing the speed of the cooling liquid and thus increasing the local Reynolds coefficient of the cooling liquid which is representative of the thermal exchanges between the cooling liquid and tube 24 and between the cooling liquid and turbulator 36.

Turbulator 36 is in contact with tube 24 at the level of the ends of teeth 45, which causes thermal exchanges between turbulator 36 and tube 24. Turbulator 36 is then advantageously formed of a material with a good thermal conductivity and takes part in the carrying off of the calories provided by the component to be cooled down. As an example, turbulator 36 may be formed of the same material as tube 24. The cross-section shown in FIG. 5 is particularly advantageous since it enables obtaining a significant thermal exchange surface area between turbulator 36 and tube 24.

More generally, the cross-section of turbulator 36 is defined according to the flow rate and to the head loss which is desired to be obtained for tube 24 while attempting to bring the thermal exchanges between turbulator 36 and tube 24 to a maximum. In the case where it is necessary to have a relatively large flow rate run through tube 24, a hollow turbulator 36 may be provided, the cooling liquid being then able to flow through turbulator 36 and around it.

Further, it is possible for turbulator 36 not to have a constant cross-section. As an example, teeth 45 may have a helical shape wound around axis D.

An example of a method for manufacturing heat sink 10 according to the present invention comprises the steps of:

-   -   forming openings 22 in body 12 of the heat sink;     -   arranging isolating sleeves 32 at the level of end openings 40         of openings 22 located on a same side of body 12;     -   arranging tubes 24 in openings 22 by inserting an end of each         tube 24 into the corresponding isolating sleeve 32, 34, which         automatically centers tube 24 with respect to opening 22 and         defines gap 26;     -   arranging a turbulator 36 in each tube 24. The diameter of tube         24 is then slightly greater than the maximum diameter of         turbulator 36 so that turbulator 36 is not in contact with tube         24, or very slightly in contact with tube 24. This eases the         insertion of turbulator 36 into tube 24 but requires the use of         a system for temporarily holding turbulator 36;     -   for each opening 22, filling gap 26 with a powder, for example,         boron nitride, through the end of opening 22 opposite to         previously-arranged isolating sleeve 32, 34;     -   compressing the powder with a piston to obtain a compact         structure exhibiting the desired thermal conductivity and         electric isolation properties. The compression causes a slight         deformation of tube 24 which then contacts turbulator 36; and     -   arranging isolating sleeves 32, 34 at the ends of openings 22         used for the powder introduction.

Inlet and exhaust manifolds 16 and 18 are then fixed to the ends of tubes 24 and isolating connections 20, 21 are arranged.

The present invention has many advantages.

First, the thermal conductivity criterion is the main criterion to be taken into account in the selection of the material forming tubes 24. The electric isolation criterion is then not to be taken into account. This enables using metal tubes 24 which keep remarkable thermal conductivity properties even for significant thicknesses. The radial thickness of the tubes then no longer is a constraint and may be determined only according to the mechanical hold that the tube must have, especially to enable its mounting on the manifolds. The compromise between a good electric isolation and a good thermal conductivity concerns the compressed powder arranged between tubes 24 and body 12 of the heat sink. However, since it is a compressed powder, there is no specific mechanical hold constraint as in the case of a conventional heat sink where the tube itself ensures the electric isolation. The radial thickness of the gap containing the compressed powder may correspond to the minimum thickness ensuring a proper electric isolation. This enables degrading as little as possible the thermal conductivity of the electric isolation layer formed by the compressed powder. In particular, for equivalent electric isolation performances, the radial thickness of the gap containing the compressed powder of a determined material is smaller than the thickness of a cooling liquid flow tube formed with the same electric isolating material implemented in a conventional heat sink.

Second, when turbulators 36 are used, they are in direct contact with associated tubes 24. Each turbulator 36 may then advantageously be formed of a material with a good thermal conductivity to take part in the thermal exchange between the cooling liquid and body 12 of the heat sink. In particular, turbulators 36 may be metallic.

Third, when turbulators 36 are used, they are maintained by the contact forces between the turbulators and the associated tubes, such contact forces being created on compression of the powder. It is thus not necessary to provide an additional turbulator hold system, which simplifies the structure of the heat sink according to the present invention.

Of course, the present invention is likely to have various alterations, modifications, and improvements which will readily occur to those skilled in the art. In particular, the thickness examples mentioned for the tubes and the gaps are given as an example and are to be adapted by those skilled in the art according to the envisaged application.

Such alterations, modifications, and improvements are intended to be part of this disclosure, and are intended to be within the spirit and the scope of the present invention. Accordingly, the foregoing description is by way of example only and is not intended to be limiting. The present invention is limited only as defined in the following claims and the equivalents thereto. 

1. A heat sink (10) comprising a body (12) made of a metallic material having a surface intended to support an electronic power component (14), the body comprising a plurality of openings (22) axially crossed by tubes (24) of circulation of a cooling liquid, each tube being formed of a material with a good thermal conductivity and being separated from the body by a ring-shaped electric isolation layer formed of a compressed powder of at least one material with good electric isolation and thermal conduction properties.
 2. The heat sink of claim 1, wherein each tube (24) is made of metal.
 3. The heat sink of claim 1, wherein the compressed powder is a boron nitride and/or aluminum nitride powder.
 4. The heat sink of claim 1, wherein the heat sink further comprises, at least in a tube (24), guiding means (36) intended to accelerate the cooling liquid flow in contact with the tube and made of a material with a good thermal conductivity.
 5. The heat sink of claim 4, wherein the guiding means (36) are maintained only by contact with the tube (24).
 6. The heat sink of claim 4, wherein the guiding means (36) comprise a cylindrical portion on the circumference of which extend grooves separated by teeth (45), the grooves being adapted to the flowing of the cooling liquid, the teeth being in contact with the tube.
 7. A method for manufacturing a heat sink (10), comprising the steps of: a) providing a heat sink body (12) made of a metallic material having a surface intended to support an electronic power component (14), the body being crossed by a plurality of openings (22); b) placing in each opening a tube (24) separated from the opening by a ring-shaped gap (26); c) filling each ring-shaped gap with a powder of at least one material with good electric isolation and thermal conduction properties; and d) compressing the powder in each gap.
 8. The method of claim 7, wherein step b) comprises, for each opening (24), the arrangement of a tubular jointing sleeve (32, 34) crossed by an orifice at one end of the opening (12), the tube being maintained in the orifice of the jointing sleeve distantly from the body, the powder being then introduced, at step c), through the ring-shaped gap (26) at the level of the axial end of the opening opposite to the jointing sleeve.
 9. The method of claim 8, wherein step d) is followed by the arrangement of an additional tubular sleeve (32, 34) at the level of the end of the opening (24) through which the powder has been introduced.
 10. The method of claim 7, comprising, before step c), the arrangement of guiding means (36) in at least one tube (24), the powder compression being performed to deform the tube so that it comes into contact with and maintains in place the guiding means. 